Discussion on power battery protection board

At present, there are all kinds of protection boards, but how to choose a good protection board is beyond everyone's grasp. However, with the general promotion of mobile power supply, the demand for load amplification is also increasing, and the discharge current is up to dozens of a, hundreds of a, or even thousands of a. Due to the advantages and disadvantages of all kinds of batteries, the secondary battery protection plate is also produced. Due to various use conditions, the technical requirements of the protection board are getting higher and higher, and the simple overcharge and discharge protection is far from meeting the current protection needs. So how to choose the protection board according to the use load?
First of all: for example, before we introduce a lithium-ion battery (lithium-ion battery nominal 3.6~3.7v, overcharge 4.25v, overcharge 2.5V), let's start from 1. Overcharge start: if we simply set an overcharge voltage protection, can it meet the requirements? As we all know, there is a polarization impedance in addition to the ohmic resistance in the resistance. When our cell is charged with a large current, a voltage drop will inevitably occur due to the existence of the resistance. The battery impedance varies from a few MR to dozens of Mr due to differences. For example, when the ohmic impedance plus polarization impedance of a cell is 30mr, then the voltage is 4. 25 when overcharged, charge at 5a, and the voltage of the battery is actually only 4. 25-0。 03*5=4。 1V, then the battery is obviously not full, which becomes more obvious with the increase of impedance. Of course, someone will ask, limit the voltage to 4. 35 is just right. However, due to the difference of batteries, when the impedance of the battery is only 10mr, then 4. 35-0。 01*5=4。 3V, then it has exceeded the standard voltage, and the battery life will be affected, reaching 4. 4V may even explode. Of course, it is a good choice to make the battery as low as possible. So how to complete this process from the protection, then we must look for this polarization impedance or adjust the charging current appropriately, when overcharge 4. 25V, with 5A charging battery voltage of 4.
1. When the current is adjusted to 2a for charging, the battery voltage is of course 4. 25-2*0。 035=4。 18. As the charging current is adjusted again, the battery can be fully charged in a short time.
2. Over release. It is appropriate to choose how much over discharge. Of course, it is no problem to choose 3V discharge, but it has been proved that only 80% of the capacity is used, and the relative time is relatively short, and it is reduced to 2 under the same conditions. 5V can be discharged for half an hour, and the impedance is more inconclusive. When you choose 10A discharge, take 30mr as an example. When you choose 3V over discharge, the battery voltage is actually 3+0 during over discharge protection. 03*10 is 3. 3V, less than 70% is used, then it is elected as 2. 5V, the actual battery voltage is 2. 8V, nearly 90%, but when a small current 1A discharge occurs, the battery voltage is actually 2. 53V, when it is discharged again, it will cross the safe discharge area. Obviously, the over discharge recovery voltage and the selection of over discharge voltage are the focus of attention.
3. The discharge current in the ordinary battery protection board is almost stable and has little change, but it changes several times in power. For example, the commonly used electric tool electric drill, for example, the electric starting instantaneous current is as high as dozens of a (different due to different power), while in normal operation, the current is only a few a to a dozen a, such as a 10. For 8V electric tools, the starting current is 50a, the idling current is 2a, and the operating current is 3~15a, so the simple overcurrent protection cannot meet the demand. When the overcurrent is more than 50a, the current of the motor is as high as 20 A during the seizure process, but the overcurrent protection current cannot be reached. Then the motor is burnt out due to too long stuck time, and due to the existence of motor inductance, the circuit may be burnt out due to excessive current and high voltage during output short circuit. When the overcurrent is taken as 15a, and the protection has been entered at the moment of startup, it is obvious that the motor cannot be started.
4. Equalization when there is discharge of multiple series of circuits, the error between batteries will inevitably occur due to discharge. When the battery pressure difference is 0. 5V, when a voltage pool has 3V over discharge protection, other batteries are 3. 5V, obviously can not fully and effectively discharge, so equalization is also an inevitable concern of multi string circuits.